I am having trouble balancing one of the half reactions:
AsO3^(-3) --> AsO4^(-4)
Which side should OH and H2O go?
Thanks.
(this is in a basic solution, by the way).
Thanks you.
Memorize these steps. They work.
1. Determine the oxidation state
As is +3 on the left; +5 on the right
and add electrons to the appropriate side to balance the change in oxdn state.
AsO3^3- ==> AsO4^3- + 2e
2. Count up the charge on left and right and add OH^- to the appropriate side to balance the charge.
Charge on left is 3-; on right is 5- so add 2OH^- to the left.
AsO3^3- + 2OH^- ==> AsO4^3- + 2e
3.Add H2O to balance the H and O (usually to the side opposite to where you added the OH^- but not always).
4. AsO3^3- + 2OH^- ==>AsO4^3- + 2e + H2O
5. Check it for
a.atoms. 1As both sides, 5 O both sides, 2 H both sides.
b. charge. -5 on the left; -5 on the right.
c. change in oxidation state. Change from +3 to +5 which is change of 2e.
Hope this helps.
By the way, if this were an ACID solution, you need change only one part of the above. In part 2 above, add J^+ instead of OH^- AND I would add a 3.5 part of "Cancel any ions common to both sides."
In the last paragraph one would add H^+ (I'm not sure what a J^+ is :-)] instead of OH^-.
To balance the half-reaction AsO3^(-3) -> AsO4^(-4), you need to follow these steps:
1. Determine the elements that are being oxidized and reduced. In this case, the oxidation state of arsenic changes from +3 to +5, so arsenic is being oxidized.
2. Write the half-reaction for the species being oxidized and the species being reduced separately.
Oxidation half-reaction: AsO3^(-3) -> AsO4^(-4)
Reduction half-reaction: To be determined
3. Balance the atoms in the half-reactions, other than oxygen and hydrogen. In this case, there is only one atom of arsenic on both sides, so no additional balancing is needed.
4. Balance the oxygen atoms by adding water (H2O) to the appropriate side of the equation. Since there are three atoms of oxygen on the left side and four on the right side, you need to add one water molecule (H2O) to the left side.
Oxidation half-reaction: AsO3^(-3) + H2O -> AsO4^(-4)
Reduction half-reaction: To be determined
5. Balance the hydrogen atoms by adding protons (H+) to the appropriate side of the equation. Since there are no hydrogen atoms on either side, you don't need to add protons.
Oxidation half-reaction: AsO3^(-3) + H2O -> AsO4^(-4)
Reduction half-reaction: To be determined
6. Balance the charges on both sides of the equation by adding electrons (e^-). The charge on the left side is -3, and the charge on the right side is -4. To balance the charges, you need to add one electron (e^-) to the left side.
Oxidation half-reaction: AsO3^(-3) + H2O + e^- -> AsO4^(-4)
Reduction half-reaction: To be determined
Now, you have balanced the oxidation half-reaction. Next, you need to determine the reduction half-reaction. Since no additional information was provided, it is not possible to determine the reduction half-reaction. You may need more information about the specific chemical reaction or context to complete the balanced equation.